Optical Properties of Crystals with Spatial Dispersion: Josephson Plasma Resonance in Layered Superconductors

We derive the transmission coefficient, $T(\omega)$, for grazing incidence of crystals with spatial dispersion accounting for the excitation of multiple modes with different wave vectors ${\bf k}$ for a given frequency $\omega$. The generalization of the Fresnel formulas contains the refraction indices of these modes as determined by the dielectric function $\epsilon(\omega,{\bf k})$. Near frequencies $\omega_e$, where the group velocity vanishes, $T(\omega)$ depends also on an additional parameter determined by the crystal microstructure. The transmission $T$ is significantly suppressed, if one of the excited modes is decaying into the crystal. We derive these features microscopically for the Josephson plasma resonance in layered superconductors.Comment: 4 pages, 2 figures, epl.cls style file, minor change

Field Dependence of the Josephson Plasma Resonance in Layered Superconductors with Alternating Junctions

The Josephson plasma resonance in layered superconductors with alternating critical current densities is investigated in a low perpendicular magnetic field. In the vortex solid phase the current densities and the squared bare plasma frequencies decrease linearly with the magnetic field. Taking into account the coupling due to charge fluctuations on the layers, we extract from recent optical data for SmLa_{1-x} Sr_x CuO_{4-delta} the Josephson penetration length lambda_{ab} approximately 1100 A parallel to the layers at T=10 K.Comment: 5 pages, 6 eps-figures, final version with minor misprints correcte

Reflectivity and Microwave Absorption in Crystals with Alternating Intrinsic Josephson Junctions

We compute the frequency and magnetic field dependencies of the reflectivity $R(\omega)$ in layered superconductors with two alternating intrinsic Josephson junctions with different critical current densities and quasiparticle conductivities for the electric field polarized along the c-axis. The parameter $\alpha$ describing the electronic compressibility of the layers and the charge coupling of neighboring junctions was extracted for the SmLa$_{1-x}$Sr$_{x}$CuO$_{4-\delta}$ superconductor from two independent optical measurements, the fit of the loss function $L(\omega)$ at zero magnetic field and the magnetic field dependence of the peak positions in $L(\omega)$. The experiments are consistent with a free electron value for $\alpha$ near the Josephson plasma frequencies.Comment: 4 pages, 4 postscript figures, misprints in table correcte

Electronic in-plane symmetry breaking at field-tuned quantum criticality in CeRhIn5

Electronic nematics are exotic states of matter where electronic interactions break a rotational symmetry of the underlying lattice, in analogy to the directional alignment without translational order in nematic liquid crystals. Intriguingly such phases appear in the copper- and iron-based superconductors, and their role in establishing high-temperature superconductivity remains an open question. Nematicity may take an active part, cooperating or competing with superconductivity, or may appear accidentally in such systems. Here we present experimental evidence for a phase of nematic character in the heavy fermion superconductor CeRhIn5. We observe a field-induced breaking of the electronic tetragonal symmetry of in the vicinity of an antiferromagnetic (AFM) quantum phase transition at Hc~50T. This phase appears in out-of-plane fields of H*~28T and is characterized by substantial in-plane resistivity anisotropy. The anisotropy can be aligned by a small in-plane field component, with no apparent connection to the underlying crystal structure. Furthermore no anomalies are observed in the magnetic torque, suggesting the absence of metamagnetic transitions in this field range. These observations are indicative of an electronic nematic character of the high field state in CeRhIn5. The appearance of nematic behavior in a phenotypical heavy fermion superconductor highlights the interrelation of nematicity and unconventional superconductivity, suggesting nematicity to be a commonality in such materials